An oscillating wing is disclosed in U.S. patent application Ser. No. 12/266,553 to Platzer et al (2008): an unstable pivoting wing with a spike is mounted on an axle with pitch control rods; this assembly is attached to a base plate with arms and switching rods. To produce oscillations this design relies on a pitch reversal spike, two pitch control rods, two arms and two switching rods. Although sails are mentioned in the above application, a pertinent sail wing design is not disclosed. A wind fin assembly, made of segmented and articulated airfoils, is disclosed in Patent Application CA2599435 to Morris (2007) and in U.S. patent application Ser. No. 11/895,568 to Morris (2007): the wind fin assembly pivots a supporting mast upon oscillation. An inflatable airfoil is mentioned in the above design; however, oscillation of the device is anticipated on the basis of a segmented and articulated assembly of airfoils, a trim bias element and a facilitating weight on a component airfoil. A flexible sheet pivotably tensioned between aligned support members is disclosed in U.S. patent application Ser. No. 11/984,850 to Gartner (2007). This design relies on the tensioned sheet imparting a limited torsional movement to the support members. Elaborate sheet tensioning spindle, telescoping adjustment and inter support member distance adjustment devices are embodied in this design. Tensioning of the sheet between aligned support members minimizes potential oscillation amplitude and effective energy capture cross section area. A vibrating membrane fixed at two ends is described in U.S. Pat. No. 7,573,143 to Frayne (2009). This design relies on the natural tendency for thin sheets of materials to flutter in the wind or aeroelastic flutter. Flutter devices are limited to small scale energy harvesting machines or sensors, largely due to the limitations of the small amplitude working membrane, low load capacity of the membrane and the requirement for securing the membrane's ends in fixed positions.
Thus, current designs in oscillating foil machines are either small scale systems with limited oscillation amplitude and power output or require additional tensioning, trimming and actuating devices or articulated foil combinations to initiate and sustain oscillations. Therefore, it is an object and advantage of the Variable Foil Machine to address the limitations in the prior art, as outlined above. Other objects and advantages of my invention will become apparent from the detailed description that follows and upon reference to the drawings.